Some of power storage systems conventionally used as emergency power supply devices or the like has a plurality of power storage devices connected in parallel in order to increase a power storage capacity. A current is input/output to/from this power storage system so as not exceed performance of the power storage devices.
A parallel-connection power storage system according to Patent Literature 1 has a plurality of switches which connect/disconnect corresponding power storage elements to/from the system, a voltage monitoring means which detects a voltage difference among the plural power storage elements, and a control means which, when the detected voltage difference is within a predetermined value in one of or a plurality of the power storage element arrays, turns on only the switch(es) corresponding to the relevant power storage element array(s), thereby preventing a trouble such as overcurrent at the time of parallel energization.
A method of abnormality detection when parallel batteries are used according to Patent Literature 2 is a method in which, in a battery parallel-connection circuit in which serially connected secondary batteries are connected in parallel, temperature of each of the batteries is detected, and based on a temperature difference between the batteries, an abnormality such as overcharge•over-discharge of the circuit is detected.
A control device of a plurality of parallel batteries sharing a load current according to Patent Literature 3 controls the plural batteries connected in parallel so that they share a load element equally.
A voltage detecting method and a voltage detecting device of parallel-connected batteries according to Patent Literature 4 use an internal resistance value of a cell, a voltage of the cell under a load, and a current value of the cell to estimate an open-circuit voltage value of each of electric cells connected in parallel.
In a method and a device of calculating a maximum charge/discharge power of a battery pack including parallel-connected batteries according to Patent Literature 5, in calculating the maximum discharge power of the battery pack, the maximum discharge power of the battery pack is calculated according to a discharge power of the parallel batteries at which a maximum discharge power of each of the parallel batteries becomes the smallest, and in calculating the maximum charge power of this battery pack, the maximum charge power of the battery pack is calculated according to a discharge power of the parallel batteries at which a maximum charge power of each of the parallel batteries becomes the smallest, whereby the maximum charge/discharge power is calculated so as to use the batteries connected in parallel in an appropriate region.
A method and a device of calculating a capacity of a parallel-connection battery pack according to Patent Literature 6 calculate internal resistances of batteries connected in parallel and add a correction coefficient thereto, thereby calculating the capacity of the battery in consideration of states of electric cells.
In a parallel battery pack according to Patent Literature 7, a switch and an internal resistance detecting means detecting an internal resistance of each battery are provided in each line of the battery, and the line where a cell whose internal resistance value is over a set value exists is disconnected, thereby preventing a decrease of a usable capacity caused by the deteriorated battery.